Sway-capable stationary bicycle

ABSTRACT

A sway capable bicycle has a bicycle frame firmly mounted on a sway-capable upper base mounted on a lower base and which has resilient members connecting each corner of the base support to the corresponding corner of the upper base.

FIELD OF THE INVENTION

The present invention relates generally to stationary cycling equipmentand specifically to improving it in order to bring closer the in-placeriding movement to the real bicycle riding on the road.

BACKGROUND ART

With reference to FIG. 1, a conventional heavy duty stationary bicycle100 comprises usually an H-shaped frame 101, comprising bars 101A, 101Band 101C, with a saddle 102 at its top back corner, a pair of handlebars103 placed at the top front corner and the two pedals crank mechanism104 placed at the middle height of the frame under the feet of therider. The pedal crank mechanism usually drives an inertial wheel 105(also called flywheel) through a transmission belt or chain 106. Theinertial wheel reduces the pedaling speed fluctuations and also throughthe transmission chain presents the rider with the controllable movementresistance provided by the braking system 107 attached to the wheel. Thebraking system can be of frictional nature or electromagnetic nature orboth. The frame 101 is mounted on a supporting base 108 (made ofhorizontal bars and/or planks) of a large enough rectangle footprint tomake the entire equipment unconditionally (i.e. absolutely) fixed in allthree planes of motion. This totally fixed nature of thestate-of-the-art stationary cycling equipment reduces to zero all thereal balance challenges any rider encounters on a real bicycle whichmoves in all three planes of motion.

With reference to FIG. 2, another state-of-the-art way of implementing astationary bicycle is to mount a real (road or mountain) bicycle 200 ona trainer 201. The trainer comprises a support 202, an electromagneticor friction braking roller 203 upon which the rear wheel of the bicycle200 rests with strong friction and a fork 204, which holds the rear axleof the bicycle 200 in a fixed position but still allowing it to freelyturn. The wheel groove support 205 for the front wheel of the bicycle200 keeps the horizontal alignment. The rider exerts the effort to workagainst the braking action of the roller 203. The end result is the sameas in the case of the stationary bicycle depicted in FIG. 1 because theroad bicycle 200 becomes absolutely fixed in all three planes of motion.The trainer 201 provides absolute support in all planes of motionsimilar to the support base 108 and acts as the variable braking systemsimilar to the braking system 107 from FIG. 1.

On a real bicycle, although being the smallest movement among the threeplanes of movement, the most difficult to control movement happens inthe frontal plane of the rider (vertical side to side sway movement).This lateral movement or sway of the rider plus bicycle system is themovement which the rider has to learn to control and minimize at alltimes to avoid crashing to the ground.

Because the goal is to minimize the lateral sway, this movement in thefrontal plane of the rider is better described as the main balancechallenge for the bicycle rider. Yet, the state-of-the-art stationarybicycle does not exhibit this challenge at all, so it does notconstitute a step in any continuous progression aimed at preparing andimproving the real bicycle riding skills. It is only a means to trainthe cardiovascular system and the endurance of the rider by the means ofthe braking resistance applied to the inertial wheel which the rider hasto overcome with the increased legs effort needed to keep the pedalsmoving. The upper body can be totally relaxed, which is not the case inreal riding, where the upper body movement is an essential part inproviding the balance of the rider and the bicycle.

SUMMARY OF THE INVENTION

A sway capable stationary bicycle base and its operation make the objectof this patent disclosure. The sway capable stationary bicycle base, asits name suggests, makes any stationary bicycle mobile and moreoverconditionally unstable in the frontal plane of the rider, i.e. thebicycle can lean from side to side, and thus confronts the rider withthe main balance challenge any real bicycle exhibits too. This isachieved in the present embodiment of this invention by placing astationary bicycle not on a solid supporting rectangular base, but on asway capable base, which comprises a base core capable to sway side toside, relative to the upright equilibrium plane of the bicycle frame, byrotating on two hinges mounted on a base support which rests on theground. The connecting medium between the base core and the base supportcan be implemented as 4 pneumatic or hydraulic struts placed in eachcorner of the base support to the corresponding corner of the base coreabove with ball-and-socket joints. The base connecting medium can alsobe implemented as a single or multiple elastic air-filled chamber(s)under variable pressure or with a waterbed viscous like structure.

The entire rider plus bicycle system exhibits an unstable equilibrium atthe upright position which challenges the rider to sway his body fromside to side to counterbalance the swaying of the bicycle itself in asimilar manner to a real road bicycle. The struts or the elasticair-filled chambers have a stiffening response at large sway angles inorder to limit the swaying to safe limits and avoid the crashing of therider sideways under the lateral component of the rider own weight. Theentire system potential energy dependence on the sway angle has theshape of a gravitational well with a raised bottom center.

The essential functionality of this invention consists in asking therider to perform a contralateral movement with the upper body inrelation to the lower body, mainly the legs, so that the rider's centerof gravity, which lies in the pelvic region, remains at all times on topof the supporting footprint of the bicycle. Or, for more advancedriders, this invention allows the rider to perform an ipsolateral (sameside) movement with the upper body in relation to the lower body, butonly if, as in real road or mountain riding, the rider sways the bicyclea lot to the opposite side.

In comparison, the state-of-the-art totally fixed bicycle allows therider to perform an ipsolateral (same side lateral) movement with theupper and lower body to increase the pressure on the pedal of that sideto make the effort easier, without requiring the upper body of the riderto sway the bicycle considerably to the opposite side. Such anipsolateral movement on a real bicycle would cause an immediate crash ifthe rider did not sway quite a lot the bicycle itself to the oppositeside, while the rider remained essentially vertical. This happenstotally unlike the stationary bicycle case, where the stationary bicyclestays vertical, but the rider sways the entire body to the same side.

Making the stationary bicycle conditionally unstable in the frontalplane of the rider brings the stationary exercise inside a continuousprogression aimed at real bicycle riding skills improvement, not justendurance and cardiovascular training. Moreover, it does not teach therider the wrong ipsolateral movement (where the bike stays vertical andthe rider sways a lot the entire body to the same side), but recruitsthe correct contralateral movement (where the bike essentially swaysvery little while the rider sways the upper body contralateral to thelower body) or the right ipsolateral movement (where the bike sways alot to one side while the body of the rider sways very little to theopposite side).

The effective gravitational pull on the rider is adjustable with thisinvention. This adjustment occurs by varying the elasticity of the baseconnecting medium in the manner that the less sway resistance the baseexhibits, the bigger the effective gravitational pull on the riderbecomes and the more difficult it is for the rider to maintain balance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a prior art conventional heavy duty stationarybicycle.

FIG. 2 is a diagram of a prior art road bicycle mounted on a trainersystem to convert it into a stationary bicycle.

FIG. 3 is a diagram of a side to side sway capable base built with 4pneumatic or hydraulic struts and this base has a conventional lightweight stationary bicycle frame mounted on top of it. FIG. 3 alsoincludes a detail showing the hinge which is capable of glidingvertically.

FIG. 4 is a diagram of a side to side and front to back sway capablebase built with 4 pneumatic or hydraulic struts and this base has aconventional light weight stationary bicycle frame mounted on top of it.FIG. 4 also includes a detail showing the cardanic cross hinge which iscapable of gliding vertically but prevents any rotation in thetransverse (horizontal) plane.

FIG. 5 is a diagram of a side to side sway capable base built with 4pneumatic or hydraulic struts and this base has a conventional heavyduty stationary bicycle frame mounted on top of it.

FIG. 6 is a simplified diagram of the forces and angles acting in thefrontal plane of the system described in FIG. 3. FIG. 6 includes also adetail showing a simplified diagram of a pneumatic strut used in theFIG. 3 system.

FIG. 7 depicts the potential energy dependence on the angulardisplacement U(∝) which has the shape of a gravitational well with araised bottom center.

FIG. 8 is a diagram of a side to side sway capable base built with 4elastic air-filled chambers and this base has a conventional lightweight stationary bicycle frame mounted on top of it. FIG. 8 alsoincludes a detail showing the simplified diagram of an elasticair-filled chamber.

FIG. 9 is a diagram of a side to side and front to back sway capablebase built with 4 elastic air-filled chambers and this base has a realroad bicycle mounted on top of it by means of a trainer assembly similarto trainer 201.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIG. 3, here is the description of a sway capable baseusing 4 hydraulic struts with a conventional light weight stationarybicycle frame mounted on top of it. The bicycle frame comprises twoconnecting horizontal bars 301 and 303, a diagonal bar 302 to insureframe rigidity, and two quasi-vertical tubes 304 and 305 a (where 305 ais prolonged by the 2 side bars 305 b and 305 c), the saddle 306 mountedon the seat tube 304 aligned back at about 20 degrees from the verticaldirection, the handlebars subassembly 307 mounted on the front tube 305a, which is aligned parallel to the seat tube 304, the two pedals andcrank arms shaft 308 with the driving sprocket 309, the chain 310, theinertial front wheel (flywheel) 311 with the gear 312 sustaining theother end of the chain 310 (where gear 312 is sustained by an axismounted between tubes 305 b and 305 c), and the electromagnetic orfrictional brake 313 mounted on bar 303.

Each of the quasi-vertical tubes of the frame, 304, 305 b and 305 c, isfixed above the middle of a horizontal lateral bar, the back one 315 andthe front one 317. Together with the horizontal bars 316 and 318, thelateral horizontal bars 315 and 317 are building together the base core,which at equilibrium is situated in the transverse (horizontal) plane.The base core is part of the base which comprises also 4 pneumatic orhydraulic struts labeled 325, 326, 327 and 328. The struts are placedthemselves on the four corners of the base support, which is similar tothe base core and has identical dimensions, and comprises side bars 319,320, 321 and 322. The struts are connected to both the base core and thebase support through ball-and-socket type of joints. In the middle ofeach of the lateral bars 315 and 317 of the base core there are thehinges 323 in the back and 324 in the front, which are fixed on theirother side respectively in the middle of the lateral bars 319 and 321 ofthe base support. The hinges 323 and 324 are sliding hinges which allowthe base core to sway side to side in the frontal plane by rotatingaround the axis 314, which connects the centers of the hinges 323 and324, but also allow the entire axis 314 to move up and down to find thebalance between the weight of the rider plus bicycle and the resistanceof the struts.

The detail on the left of FIG. 3 shows a simplified diagram of apneumatic or hydraulic strut, where the piston rod 328A glides insidethe cylinder 328B. The detail on the right of FIG. 3 shows a simplifieddiagram of the hinge 324, where the hinge head 324A rotates on the axissupported by the fork 324B. The fork 324B is fixed on the piston rod324C which glides inside the cylinder 324D.

With reference to FIG. 4, any item labeled 4 xx corresponds to the item3 xx on FIG. 3 with the following exceptions. The hinges 323 and 324 arereplaced by the cardanic cross hinge 430, which is detailed on the rightof FIG. 4, and comprises the hinge head 430A which can sway in twoplanes on the cardanic cross supported by the fork 430B. The fork 430Bis fixed on top of the piston bar 430C which glides inside the pump body430D. The cardanic cross hinge must have the piston rod 430C and thepump body 430D with a rectangular cross-section in order to prevent anyrotation in the horizontal plane. Any rotation in the horizontal planeof the bicycle frame in FIG. 4 would lead to an immediate crash of theentire system, because the struts 425 to 428 are mounted withball-and-socket joints and cannot take any rotational effort. This iswhy the cross-sectional area of the hinge head 430A and the rest of thehinge 430 have to be big enough to be able to withstand the torque inthe horizontal plane transmitted through the frame bar 403.

With reference to FIG. 5, one can see that the heavy duty conventionalstationary bicycle frame of FIG. 1 is mounted on the side to side swaycapable base of FIG. 3. The main purpose of this FIG. 5 is to show thata heavy frame will not provide a close riding experience to a real roadbike, mainly because of the greater inertia of the frame itself and alsoof the flywheel. The struts 525 to 528 have to be accordingly muchstronger than the struts 325 to 328 of FIG. 3 where the sway capablebase is supporting a light weight bicycle frame.

With reference to FIG. 6, the simplified dynamics of the lateral sway ofthe rider plus bicycle system can be expressed in terms of the masscenter torque equation. The stability of the rider plus the bicyclesystem is ensured if the resulting torque in the frontal plane actsopposite of the angular displacement and thus brings back the rider tothe vertical position.

The rider plus bicycle system has the mass center C at the distance Hfrom the pivoting point O which lies on the middle axis 314 of the basecore and at equal distance L from the side bars 316 and 318. Because thesway happens only in the frontal plane, the two struts on the left sideof the rider can be lumped together into strut SL and the two struts onthe right side of the rider can be lumped together into strut SR. Theequivalent strut SL acts on the middle point of bar 316 labeled A₁ andequivalent strut SR acts on the middle point of bar 318 labeled A₂. Ofcourse, the 4 corner struts 325 to 328 can be replaced also for realwith just the two struts SL and SR in another version of the inventionembodiment in FIG. 3, but with less reliability.

The gravity force G decomposes into a normal component (not shown andcompensated by the hinges) and a lateral component G_(L), depending uponthe angle α between the segment OC and the vertical axis OY. The forcesG and G_(L) enclose the angle π/2−α, so the following relationshipholds:G _(L) =G*sin ∝  (Eq. 1)Because the angle between the segment OA₁ of length L and the horizontalaxis OX is also α, the displacement y of the strut SL equals:y=L*sin ∝  (Eq. 2)Let us consider the torques around the axis OZ (which is also axis 314on FIG. 3). Because of the angular displacement α, strut SL exhibits theforce R₁ and strut SR exhibits the force R₂, which create torquesopposing to the torque created by the lateral component G_(L) ofgravity. Because G_(L) has segment OC of length H as its arm, R₁ hassegment OA₁ of length L as its arm and R₂ has segment OA₂ of length L asits arm, the total torque acting on the rider plus bicycle system is:M=G _(L) *H−(R ₁ *L+R ₂ *L)   (Eq. 3)

In order to express the forces R₁ and R₂ in terms of the angulardisplacement, with reference to the detail in FIG. 6, the simplifieddiagram of the strut SL considers it as an air-filled cylinder underpressure, having at rest the length h, pressure p0 and volume V0. Restis defined the rider plus bicycle upright position where α=0, so h isnot the zero force resting length of the strut, but rather the restinglength of the strut under the force G/2 (since there are two struts inthe system). This is possible because the hinges 323 and 324 are slidinghinges which allow the axis OZ (314) to adjust up or down depending onG.

The strut cross-sectional area is S. The linear displacement of thestrut is y and it is given by equation 2 mentioned above.

The volume V(y) of the strut is given by the following equation:V(y)=S*(h−y)   (Eq. 4)The pressure p(y) on the strut is related to the force F(y) acting onthe strut:p(y)=F(y)/S   (Eq. 5)From the general gas law the following equation holds:p(y)*V(y)=p0*V0   (Eq. 6)By replacing the terms in Equation 6 one obtains:p(y)*V(y)=F(Y)/S*S*(h−y)=F(y)*(h−y)=p0*V0Same holds for y=0 also, so one obtains:F(0)*(h−0)=F0*h=p0*V0As explained above F0 is the resting force on the strut:F(0)=F0=G/2   (Eq. 7)Finally one obtains the expression for F(y):F(y)*(h−y)=F0*hF(y)=F0*h/(h−y)   (Eq. 8)One obtains now the expression for R₁(y):R ₁(y)=F(y)−F0=F0*h/(h−y)−F0=F0*y/(h−y)R ₁(y)=F0*y/(h−y)   (Eq. 9)By anti-symmetry around the origin O one obtains:R ₂(y)=−R1(−y)=−F0*(−y)/(h+y)R ₂(y)=F0*y/(h+y)   (Eq. 10)Going back to the torque equation 3 and replacing G_(L), R₁ and R₂ interms of the strut linear displacement y, the following calculationshold:M=G _(L) *H−(R ₁ *L+R ₂ *L)M=G*y/L*H−L*(F0*y/(h−y)+F0*y/(h+y))Remembering that F0=G/2 one obtains further:

$M = {{G*{H/L}*y} - {{G/2}*L*\frac{2*h*y}{h^{2} - y^{2}}}}$Because the system sway is limited to small angular displacements onecan use the following approximation:y=L*sin ∝≅L*∝  (Eq. 11)This greatly simplifies the torque expression:

$\begin{matrix}{M = {{G*{H/L}*L*} \propto {{- G}*L*\frac{{h*L*} \propto}{{h^{2} - {L^{2}*}} \propto^{2}}}}} & \left( {{Eq}.\mspace{14mu} 12} \right)\end{matrix}$One defines the maximum angular displacement as:∝_(max) =h/L<<1   (Eq. 13)The definition is justified by the fact that the strut resistance goesto infinite when a approaches ∝_(max), so the rider and bicycle systemare protected against crashing. Furthermore, the value is much smallerthan 1, which justifies again the approximation made in equation 11.Replacing equation 13 in 12 one obtains the final expression for thetotal torque:M(α)=G*H*∝−G*h*∝/(∝_(max) ²−∝²)   (Eq. 14)The torque depends only on the angular displacement α and not on thepast trajectory, which means that our system is conservative (since wehave neglected all friction in the frontal plane). This allows thecomputation of the potential energy:

$\begin{matrix}{{M( \propto )} = {- \frac{\mathbb{d}{U( \propto )}}{\mathbb{d} \propto}}} & \left( {{Eq}.\mspace{14mu} 15} \right)\end{matrix}$Choosing U(0)=0 one obtains:U(∝)=−∫₀ ^(∝) M(u)*du   (Eq. 16)With the variable substitution:

$\frac{u*{du}}{\propto_{\max}^{2}{- \propto^{2}}} = {{{- \frac{1}{2}}*\frac{d\left( {\propto_{\max}^{2}{- \propto^{2}}} \right)}{\propto_{\max}^{2}{- \propto^{2}}}} = {{- \frac{1}{2}}*d\;{\ln\left( {\propto_{\max}^{2}{- \propto^{2}}} \right)}}}$One obtains the final expression for the potential energy:

$\begin{matrix}{{U( \propto )} = {{{- \frac{1}{2}}*G*H*} \propto^{2}{{+ \frac{1}{2}}*G*h*{\ln\left( \frac{\propto_{\max}^{2}}{\propto_{\max}^{2}{- \propto^{2}}} \right)}}}} & \left( {{Eq}.\mspace{14mu} 17} \right)\end{matrix}$For α very close to zero, one can approximate:

$\begin{matrix}{{\ln\left( \frac{\propto_{\max}^{2}}{\propto_{\max}^{2}{- \propto^{2}}} \right)} \cong \frac{\propto^{2}}{\propto_{\max}^{2}}} & \left( {{Eq}.\mspace{14mu} 18} \right)\end{matrix}$This allows one to obtain the potential energy simplified equationaround the upright position (zero angular displacement):

$\begin{matrix}{{U( \propto )} = {{{- \frac{1}{2}}*G*H*} \propto^{2}{*\left( {1 - \frac{L^{2}}{h*H}} \right)}}} & \left( {{Eq}.\mspace{14mu} 19} \right)\end{matrix}$In order to create the unstable equilibrium in the upright position thefollowing equation must hold:

$\begin{matrix}{{1 - \frac{L^{2}}{h*H}} > {0\mspace{14mu}{or}\text{:}\mspace{14mu} L^{2}} < {h*H}} & \left( {{Eq}.\mspace{14mu} 20} \right)\end{matrix}$When equation 20 holds, the potential energy U(∝) exhibits the behaviorof a gravitational well with a raised bottom center, which means thatthe rider has an unconditionally unstable upright position, like on areal bicycle, but has on both sides unconditionally stable endpositions, which resemble essentially training wheels on both sides ofthe bicycle. The graph of the potential energy U(∝) is depicted in FIG.7. Equation 20 predicts that if L is increased, then the uprightequilibrium becomes unconditionally stable, which makes sense becausethe strut resistance gets a bigger contribution into the torquesummation.

It is of great importance that the hinges 323 and 324 allow the basecore (315, 316, 317 and 318) to slide vertically and as such allow thestruts to find the equilibrium position where Equation 7 holds. Equation7 states that the equilibrium position of the bicycle self-adjusts forthe rider's weight. Moreover, the elasticity of the struts self-adjustsaccording to the rider's weight. If the hinges 323 and 324 had beensimple hinges with a fixed axis, not vertically gliding, then the strutswould have had to be adjusted according to the rider's weight: morepressure (i.e. higher resistance) for a heavier rider. With the glidinghinges, the struts self-adjust to a higher pressure setting for aheavier rider because they support the bigger weight even in the restingposition. With non-gliding hinges, the struts combined force F0 must bemade equal to G by external pressure adjustment, so that the strutresistance forces R₁ and R₂ will maintain their matching to G_(L) (whichis proportional to G). This would have been more complicated andcumbersome for the rider than using gliding hinges for the constructionof this invention.

With reference to FIG. 8, the system of FIG. 4 is built using elasticair-filled chambers 825, 826, 827 and 828 which replace the struts 425to 428. In a similar way, the struts 325 to 328 of FIG. 3 could bereplaces by elastic air-filled chambers. The main reasons for replacingstruts with elastic air-filled chambers are cost reduction andsimplified construction. The elastic air-filled chambers attach directlywith screws to the base core and the base support, so that no expensiveball-and-socket joints are needed as in the case of struts. On thedownside, elastic air-filled chambers are less reliable than struts andalso they cannot support as much weight as the struts can, which meansthat air-filled chambers can be used only for light bicycle frames andmore important only for light riders.

The detail on the right of FIG. 8 shows a simplified diagram of theelastic air-filled chamber 828 in order to deduce its force response Fto the displacement y.V0=h*π*r ²   (Eq. 21)V=V(y)=(h−y)*π*(r+x)²   (Eq. 22)p*V=p0*V0   (Eq. 23)F=F(y)=p*π*(r+x)²   (Eq. 24)Let us replace V from Eq. 22 into Eq. 23:p*(h−y)*π*(r+x)²=(h−y)*[p*π*(r+x)² ]p0*V0   (Eq. 25)We can use Eq. 24 to replace F into Eq. 25:(h−y)*F=p0*V0=(h−0)*F(0)=h*F0   (Eq. 26)We obtain finally:

$\begin{matrix}{{\Delta\; F} = {{F - {F\; 0}} = {{{F\; 0*\frac{h}{h - y}} - {F\; 0}} = {F\; 0*{y/\left( {h - y} \right)}}}}} & \left( {{Eq}.\mspace{14mu} 27} \right)\end{matrix}$Equation 27 is the same as equation 9 because ΔF is identical to R₁:R ₁(y)=F0*y/(h−y)   (Eq. 9)This allows us to conclude that the rest of the analysis on FIG. 6applies also for the system FIG. 8, which displays the same behavior asthe gravitational well with a raised bottom center.

FIG. 9 is a diagram of a side to side and front to back sway capablebase built with 4 elastic air-filled chambers and this base has a realroad bicycle mounted on top of it by means of a trainer assembly similarto trainer 201 in FIG. 2, with the exception that the trainer fork 903is attached directly to the base core back side bar 915.

1. A sway-capable stationary bicycle comprising: a substantially planarupper support structure having a length, a width and four cornersdefining a rectangle, presenting a front edge and a back edge each ofthe width of the structure; a bicycle frame symmetrical about asubstantially vertical frame plane, the frame including a lowersubstantially horizontal frame member rigidly joined to the uppersupport structure with the lower horizontal frame member in the plane ofthe upper support structure and bisecting the plane of the upper supportstructure along its length; a substantially planar lower supportstructure of the same length and width of the upper support structure,also presenting a front edge and a back edge, the lower supportstructure positioned with each corner directly below each correspondingcorner of the upper support structure; four resilient members of acommon relaxed height, one member at each corner joined to the upper andlower support structure, spacing the upper and lower support structuresapart by an equilibrium height determined by the combined weight of theupper structures and a rider if mounted; a first vertically-orientedstabilizing member constrained to translate only vertically, presentinga hinge at an upper end with a horizontal hinge axis, the hinge rigidlyjoined to the underside of the front edge of the upper support structureat substantially the center of the width, in a manner to direct thehinge axis in the length direction of the support structure, below thesupport structure; and a second vertically-oriented stabilizing memberconstrained to translate only vertically, presenting a hinge at an upperend with a horizontal hinge axis, the hinge rigidly joined to theunderside of the rear edge of the upper support structure atsubstantially the center of the width, in a manner to direct the hingeaxis in the length direction of the support structure; wherein the hingeaxes form a lengthwise axis about which the frame plane of the bicycleframe may rotate within the constraints of the comer resilient members,and the two stabilizing members keep the upper and the lower supportstructures substantially aligned vertically.
 2. The stationary bicycleof claim 1 wherein the corner resilient members are one of pneumatic orhydraulic cylinders joined in a universally pivotable manner to each ofthe upper and lower frame structures, enabled to present a relaxedlength and to produce a resistant force when forced by movement tocontract in length.
 3. The stationary bicycle of claim 1 wherein thestabilizing members are constrained to translate only vertically each bya guide rigidly joined to the front or rear edges of the lower supportstructure at substantially the center of the width.
 4. The stationarybicycle of claim 1 wherein the corner resilient members are elastic,air-filled chambers.
 5. A sway-capable stationary bicycle comprising: asubstantially planar upper support structure having a length, a widthand four corners defining a rectangle, presenting a front edge and aback edge each of the width of the structure; a bicycle framesymmetrical about a substantially vertical frame plane, the frameincluding a lower substantially horizontal frame member rigidly joinedto the upper support structure with the lower horizontal frame member inthe plane of the upper support structure and bisecting the plane of theupper support structure along its length; a substantially planar lowersupport structure of the same length and width of the upper supportstructure, also presenting a front edge and a back edge, the lowersupport structure positioned with each comer directly below eachcorresponding comer of the upper support structure; four resilientmembers of a common relaxed height, one member at each comer joined tothe upper and lower support structure, spacing the upper and lowersupport structures apart by an equilibrium height determined by thecombined weight of the upper structures and a rider if mounted; avertically-oriented stabilizing member constrained to translate onlyvertically and to prevent rotation in the horizontal plane, the memberpresenting a cardanic cross hinge at an upper end with one horizontalhinge axis in the direction of the length and the other in the directionof the width of the support structures, the cardanic hinge joined to theunderside of the upper support structure at a point substantially at thecenter of the rectangle defined by the comers, and to the upper side ofthe lower support structure also at substantially the center of therectangle defined by the comers; wherein the hinge axes constrain theupper support structure to rotate in any direction about the cardanichinge axes within the constraints of the comer resilient members, andthe stabilizing member keeps the upper and the lower support structuressubstantially aligned vertically.
 6. The stationary bicycle of claim 5wherein the corner resilient members are one of pneumatic or hydrauliccylinders joined in a universally pivotable manner to each of the upperand lower frame structures, enabled to present a relaxed length and toproduce a resistant force when forced by movement to contract in length.7. The stationary bicycle of claim 5 wherein the corner resilientmembers are elastic, air-filled chambers.